“I want to convert John Miedema’s OpenBook Book Data plugin for Wordpress into this kind of module for Drupal but really don’t have a good enough understanding of Drupal to write the necessary code at this point. Doing something similar with OCLC numbers and WorldCat Search API would be cool too.”

Done! I’m putting the finishing touches on it but here is the code:
http://github.com/rubinsztajn/book-post-module/tree/master/openlibrary.module

I’d eventually like to turn it into a module that includes other kinds of functionality that might be helpful when including posts about books in Drupal, e.g incorporating the Google embedded viewer api, frbr-like edition matching using LibraryThing’s thingISBN, and OpenLibrary search API.

I’ll let you know when the module is ready for download.